% underscore.sty     12-Oct-2001   Donald Arseneau   asnd@triumf.ca% Make the "_" character print as "\textunderscore" in text.% Copyright 1998,2001 Donald Arseneau;  Distribute freely if unchanged.% Instructions follow after the definitions. \ProvidesPackage{underscore}[2001/10/12] \begingroup \catcode`\_=\active \gdef_{% \relax % No relax gives a small vulnerability in alignments   \ifx\if@safe@actives\iftrue % must be outermost test!      \string_%   \else      \ifx\protect\@typeset@protect         \ifmmode \sb \else \BreakableUnderscore \fi      \else         \ifx\protect\@unexpandable@protect \noexpand_%         \else \protect_%      \fi\fi    \fi}\endgroup % At begin: set catcode; fix \long \ttdefault so I can use it in comparisons; \AtBeginDocument{%  {\immediate\write\@auxout{\catcode\number\string`\_ \string\active}}%  \catcode\string`\_\string=\active  \edef\ttdefault{\ttdefault}%} \newcommand{\BreakableUnderscore}{\leavevmode\nobreak\hskip\z@skip \ifx\f@family\ttdefault \string_\else \textunderscore\fi \usc@dischyph\nobreak\hskip\z@skip} \DeclareRobustCommand{\_}{%  \ifmmode \nfss@text{\textunderscore}\else \BreakableUnderscore \fi} \let\usc@dischyph\@dischyph\DeclareOption{nohyphen}{\def\usc@dischyph{\discretionary{}{}{}}}\DeclareOption{strings}{\catcode`\_=\active} \ProcessOptions\ifnum\catcode`\_=\active\else \endinput \fi %%%%%%%%   Redefine commands that use character strings   %%%%%%%% \@ifundefined{UnderscoreCommands}{\let\UnderscoreCommands\@empty}{}\expandafter\def\expandafter\UnderscoreCommands\expandafter{%  \UnderscoreCommands  \do\include \do\includeonly  \do\@input \do\@iinput \do\InputIfFileExists  \do\ref \do\pageref \do\newlabel  \do\bibitem \do\@bibitem \do\cite \do\nocite \do\bibcite} % Macro to redefine a macro to pre-process its string argument% with \protect -> \string.\def\do#1{% Avoid double processing if user includes command twice! \@ifundefined{US\string_\expandafter\@gobble\string#1}{%   \edef\@tempb{\meaning#1}% Check if macro is just a protection shell...   \def\@tempc{\protect}%   \edef\@tempc{\meaning\@tempc\string#1\space\space}%   \ifx\@tempb\@tempc % just a shell: hook into the protected inner command     \expandafter\do       \csname \expandafter\@gobble\string#1 \expandafter\endcsname   \else % Check if macro takes an optional argument     \def\@tempc{\@ifnextchar[}%     \edef\@tempa{\def\noexpand\@tempa####1\meaning\@tempc}%     \@tempa##2##3\@tempa{##2\relax}%     \edef\@tempb{\meaning#1\meaning\@tempc}%     \edef\@tempc{\noexpand\@tempd \csname        US\string_\expandafter\@gobble\string#1\endcsname}%     \if \expandafter\@tempa\@tempb \relax 12\@tempa % then no optional arg       \@tempc #1\US@prot     \else  % There is optional arg       \@tempc #1\US@protopt     \fi   \fi }{}} \def\@tempd#1#2#3{\let#1#2\def#2{#3#1}} \def\US@prot#1#2{\let\@@protect\protect \let\protect\string  \edef\US@temp##1{##1{#2}}\restore@protect\US@temp#1}\def\US@protopt#1{\@ifnextchar[{\US@protarg#1}{\US@prot#1}}\def\US@protarg #1[#2]{\US@prot{{#1[#2]}}} \UnderscoreCommands\let\do\relax \let\@tempd\relax  % un-do %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \endinput underscore.sty    12-Oct-2001  Donald Arseneau Features:~~~~~~~~~\_ prints an underscore so that the hyphenation of constituent wordsis not affected and hyphenation is permitted after the underscore.For example, "compound\_fracture" hyphenates as com- pound_- frac- ture.If you prefer the underscore to break without a hyphen (but still with the same rules for explicit hyphen-breaks) then use the [nohyphen]package option. A simple _  acts just like \_ in text mode, but makes a subscript in math mode: activation_energy $E_a$ Both forms use an underscore character if the font encoding containsone (e.g., "\usepackage[T1]{fontenc}" or typewriter fonts in any encoding),but they use a rule if the there is no proper character. Deficiencies:~~~~~~~~~~~~~The skips and penalties ruin any kerning with the underscore character(when a character is used).  However, there doesn't seem to be much, ifany, such kerning in the ec fonts, and there is never any kerning witha rule. You must avoid "_" in file names and in cite or ref tags, or you must use the babel package, with its active-character controls, or you must give the [strings] option, which attempts to redefine several commands (and may not work perfectly).  Even without the [strings] option or babel, you can use occasional underscores like: "\include{file\string_name}". Option: [strings]~~~~~~~~~~~~~~~~~The default operation is quite simple and needs no customization; butyou must avoid using "_" in any place where LaTeX uses an argument asa string of characters for some control function or as a name.  Theseinclude the tags for \cite and \ref, file names for \input, \include,and \includegraphics, environment names, counter names, and placementparameters (like "[t]").  The problem with these contexts is that theyare `moving arguments' but LaTeX does not `switch on' the \protectmechanism for them. If you need to use the underscore character in these places, the packageoption [strings] is provided to redefine commands taking a string argumentso that the argument is protected (with \protect -> \string).  The listof commands is given in "\UnderscoreCommands", with "\do" before each,covering \cite, \ref, \input, and their variants.  Not included are manycommands regarding font names, everything with counter names, environmentnames, page styles, and versions of \ref and \cite defined by externalpackages (e.g. \vref and \citeyear). You can add to the list of supported commands by defining \UnderscoreCommandsbefore loading this package; e.g.    \usepackage{chicago}   \newcommand{\UnderscoreCommands}{%   (\cite already done)     \do\citeNP \do\citeA \do\citeANP \do\citeN \do\shortcite     \do\shortciteNP \do\shortciteA \do\shortciteANP \do\shortciteN     \do\citeyear \do\citeyearNP   }   \usepackage[strings]{underscore} Not all commands can be supported this way!  Only commands that take astring argument *first* can be protected.  One optional argument beforethe string argument is also permitted, as exemplified by \cite: both\cite{tags} and \cite[text]{tags} are allowed.  A command like\@addtoreset which takes two counter names as arguments could notbe protected by adding it to \UnderscoreCommands. !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! When you use the [strings] option, you must load this package !!!! last (or nearly last).                                        !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! There are two reasons: 1) The redefinitions done for protection must comeafter other packages define their customized versions of those commands.2) The [strings] option requires the _ character to be activated immediatelyin order for the cite and ref tags to be read properly from the .aux fileas plain strings, and this catcode setting might disrupt other packages. The babel package implements a protection mechanism for many commands,and will be a complete fix for most documents without the [strings] option.Many add-on packages are compatible with babel, so they will get thestrings protection also.  However, there are several commands that are not covered by babel, but can easily be supported by the [strings] and \UnderscoreCommands mechanism.  Beware that using both [strings] and babel may lead to conflicts, but does appear to work (load babel last). Implementation Notes:~~~~~~~~~~~~~~~~~~~~~The first setting of "_" to be an active character is performed in a localgroup so as to not interfere with other packages.  The catcode settingis repeated with \AtBeginDocument so the definition is in effect for thetext.  However, the catcode setting is repeated immediately when the[strings] option is detected. The definition of the active "_" is essentially:       \ifmmode \sb \else \BreakableUnderscore \fiwhere "\sb" retains the normal subscript meaning of "_" and where"\BreakableUnderscore" is essentially "\_".  The rest of the definitionhandles the "\protect"ion without causing \relax to be inserted beforethe character. \BreakableUnderscore uses "\nobreak\hskip\z@skip" to separate theunderscore from surrounding words, thus allowing TeX to hyphenate them,but preventing free breaks around the underscore. Next, it checks thecurrent font family, and uses the underscore character from tt fonts orotherwise \textunderscore (which is a character or rule depending onthe font encoding).  After the underscore, it inserts a discretionaryhyphenation point as "\usc@dischyph", which is usually just "\-"except that it still works in the tabbing environment, although itwill give "\discretionary{}{}{}" under the [nohyphen] option.  Afterthat, another piece of non-breaking interword glue is inserted. Ordinarily, the comparison "\ifx\f@family\ttdefault" will always fail because \ttdefault is `long' where \f@family is not (boooo hisss), but \ttdefault is redefined to be non-long by "\AtBeginDocument". The "\_" command is then defined to use "\BreakableUnderscore". If the [strings] option is not given, then that is all! Under the [strings] option, the list of special commands is processed to:- retain the original command as \US_command (\US_ref)- redefine the command as \US@prot\US_command for ordinary commands  (\ref -> \US@prot\US_ref) or as \US@protopt\US_command when an optional  argument is possible (\bibitem -> \US@protopt\US_bibitem).- self-protecting commands (\cite) retain their self-protection.Diagnosing the state of the pre-existing command is done by painfulcontortions involving \meaning. \US@prot and \US@protopt read the argument, process it with \protectenabled, then invoke the saved \US_command. Modifications:~~~~~~~~~~~~~~12-Oct-2001  Babel (safe@actives) compatibility and [nohyphen] option. Test file integrity:  ASCII 32-57, 58-126:  !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~